The present invention relates to a fine-line pattern forming method for use in a manufacturing process for a semiconductor IC device and the like, and a material for forming a pattern used in the pattern forming method.
In the manufacture of ICs, LSIs and the like, a pattern is conventionally formed through photolithography using UV, in which a light source with a shorter wavelength has become mainly used in accordance with refinement of a semiconductor device. Recently, a surface imaging process using dry development has been developed in order to increase the depth of focus and improve practical resolution in using a light source with a shorter wavelength.
As an example of the surface imaging process, U.S. Pat. No. 5,278,029 discloses a method in which, after selectively forming a polysiloxane film on the surface of a resist film of a resist material which can generate an acid through exposure, the resist film is dry etched by using the polysiloxane film as a mask, so as to form a resist pattern.
Now, this conventional method of forming the resist pattern will be described with reference to FIGS. 5(a) through 5(d).
In this method, a copolymer of 1,2,3,4-tetrahydronaphthyridinenimino-p-styrene sulfonate (NISS) and methyl methacrylate (MMA) is used as the resist material for generating an acid through exposure.
First, as is shown in FIG. 5(a), a resist film 401, which generates an acid through exposure, coated on a semiconductor substrate 400 is irradiated with a KrF excimer laser 404 by using a mask 403, and thus, the acid is generated in an exposed area 401a of the resist film 401. Owing to this acid, the exposed area 401a is changed to be hydrophilic, so that water in air can be easily adsorbed by the exposed area 401a. As a result, a thin water absorbing layer 405 is formed in the vicinity of the surface of the exposed area 401a as is shown in FIG. 5(b).
Next, when an alkoxysilane gas 406 is introduced onto the surface of the resist film 401, the acid generated on the surface of the exposed area 401a works as a catalyst, so that alkoxysilane is hydrolyzed and dehydrated. As a result, an oxide film 407 is formed on the surface of the exposed area 401a as is shown in FIG. 5(c). Subsequently, when the resist film 401 is dry etched by RIE using O2 plasma 408 by using the oxide film 407 as a mask, a fine-line resist pattern 409 is formed as is shown in FIG. 5(d).
This pattern forming method thus adopts a negative type lithography process for forming a resist pattern in an exposed area, in which the acid generated in the exposed area of the resist film is used as the catalyst for selectively forming the oxide film in the exposed area and the oxide film is used as a mask in the dry etching for forming the resist pattern.
The negative type lithography process has the following problems in, for example, forming a contact hole for connecting multilayered interconnections of an IC:
First, usage of a mask generally adopted in pattern exposure can cause the following problem: In the lithography for forming a contact hole, the aperture ratio of the mask is very high when the negative lithography process is used. Specifically, while a light shielding film against exposing light is formed merely in a portion corresponding to the contact hole on the mask, the light shielding film is removed and quartz of the mask substrate is bare in the other portion excluding the contact hole in order to transmit the exposing light. Since the area occupied by all the contact holes in the entire area of a semiconductor chip is generally very small, the proportion of the area occupied by the bare quartz to the area of the light shielding film on the mask becomes high, namely, the aperture ratio of the mask becomes high.
When the aperture ratio of the mask is high, the effect of ambient dusts is increased. Specifically, dusts adhered to the light shielding film on the mask scarcely affect the process, but those adhered to the transparent portion of the mask change this portion into a light shielding portion. When the exposure is effected by using the mask to which dusts are thus adhered, a pattern defect is caused in the portion to which the dusts are adhered. In this manner, since the aperture ratio of the mask is high in the negative type lithography process, the process can be easily affected by dusts, resulting in easily decreasing the yield.
Secondly, in the lithography process for forming a contact hole, a half-tone type mask can be used for the purpose of increasing the depth of focus. However, the effect of increasing the depth of focus can be attained merely in a positive type lithography but cannot be attained in the negative type lithography. Accordingly, in the formation of a contact hole, the depth of focus is smaller in the negative type process than in the positive type process.
The occurrence of these first and second problems are not limited to the formation of a contact hole, but can be caused in the cases where a mask having a larger area of the transparent portion is used and where the depth of focus is desired to be increased.
In view of the aforementioned conventional problems, the object of the invention is realizing a positive type surface imaging process replaceable with the negative type surface imaging process.
In order to achieve this object, a resist film including an acidic or a basic group is selectively irradiated with an energy beam in this invention, so that a basic or an acidic group having the reverse property to that of the group included in the resist film can be generated in an exposed area. Alternatively, after generating an acidic or a basic group in an exposed area by selectively irradiating a resist film with an energy beam, the entire surface of the resist film is irradiated with another energy beam, so that a basic or an acidic group having the reverse property to that of the group generated in the exposed area can be generated on the entire surface of the resist film. Thus, neutralization is effected in the exposed area of the resist film, and in an unexposed area of the resist film, the acidic or the basic group works as a catalyst for forming an oxide film. In this manner, a positive type surface imaging process, which cannot be attained by the conventional method, can be realized by this invention.
The first pattern forming material of this invention comprises a copolymer including a first group for generating a base through irradiation with an energy beam and a second group having an acidic property.
When the resist film formed out of the first pattern forming material is selectively irradiated with the energy beam, the first group is dissolved into the base in the exposed area on the resist film, so that the generated base is neutralized with the second group having the acidic property, while the unexposed area on the resist film remains to be acidic. Accordingly, since merely the unexposed area on the resist film can selectively retain its acidic property, the positive type surface imaging process can be realized.
The second group in the first pattern forming material is preferably a group including a sulfonic acid group. In this case, owing to the strong acidic property of sulfonic acid, sulfonic acid can exhibit its strong catalytic function in the formation of the metal oxide film in the unexposed area on the resist film. Therefore, the strong acidic property can be selectively retained merely in the unexposed area on the resist film.
The copolymer in the first pattern forming material is preferably a binary copolymer represented by the following general formula or a ternary or higher copolymer obtained by further polymerizing the binary copolymer with another group: 
wherein R1 indicates a hydrogen atom or an alkyl group; R2 and R3 independently indicate a hydrogen atom, an alkyl group, a phenyl group or an alkenyl group, or together indicate a cyclic alkyl group, a cyclic alkenyl group, a cyclic alkyl group having a phenyl group or a cyclic alkenyl group having a phenyl group; R4 indicates a hydrogen atom or an alkyl group; x satisfies a relationship of 0 less than x less than 1; and y satisfies a relationship of 0 less than y less than 1.
In this case, since sulfonic acid can exhibit its strong catalytic function in the formation of the metal oxide film in the unexposed area on the resist film, the strong acidic property can be selectively retained in the unexposed area on the resist film. On the other hand, in the exposed area on the resist film, since amine having a strong basic property is generated, sulfonic acid having a strong acidic property can be completely neutralized. Accordingly, the strong acidic property can be selectively retained merely in the unexposed area on the resist film.
The second pattern forming material of this invention comprises a copolymer including a first group for generating an acid through irradiation with an energy beam and a second group having a basic property.
When the resist film formed out of the second pattern forming material is selectively irradiated with the energy beam, the first group is dissolved into the acid in the exposed area on the resist film, so that the generated acid can be neutralized with the second group having the basic property, while the unexposed area on the resist film remains to be basic. Accordingly, merely the unexposed area on the resist film can selectively retain the basic property, resulting in realizing the positive type surface imaging process.
The first group in the second pattern forming material is preferably a group for generating sulfonic acid. In this case, owing to the strong acidic property of sulfonic acid, the exposed area on the resist film can be completely neutralized, while the unexposed area on the resist film remains to be basic. Accordingly, the unexposed area of the resist film can selectively retain the basic property.
The copolymer in the second pattern forming material is preferably a binary copolymer represented by the following general formula or a ternary or higher copolymer obtained by further polymerizing the binary copolymer with another group: 
wherein R5 indicates a hydrogen atom or an alkyl group; R6 and R7 independently indicate a hydrogen atom, an alkyl group, a phenyl group or an alkenyl group, or together indicate a cyclic alkyl group, a cyclic alkenyl group, a cyclic alkyl group having a phenyl group or a cyclic alkenyl group having a phenyl group; R8 indicates a hydrogen atom or an alkyl group; x satisfies a relationship of 0 less than x less than 1; and y satisfies a relationship of 0 less than y less than 1.
In this case, amine can exhibit its strong catalytic function in the formation of the metal oxide film in the unexposed area on the resist film, so that the unexposed area on the resist film can selectively retain the strong basic property. On the other hand, in the exposed area of the resist film, since sulfonic acid having a strong acidic property is generated, amine having a strong basic property can be completely neutralized. Accordingly, merely the unexposed area on the resist film can selectively retain the strong basic property.
The third pattern forming material of this invention comprises a copolymer including a first group for generating an acid through irradiation with a first energy beam having a first energy band; and a second group for generating a base through irradiation with a second energy beam having a second energy band different from the first energy band.
In the resist film formed out of the third pattern forming material, the acid is generated through the irradiation with the first energy beam, and the base is generated through the irradiation with the second energy beam. Accordingly, when the pattern exposure of the resist film using the first energy beam is effected and then the entire surface exposure using the second energy beam is effected, in the exposed area of the first energy beam on the resist film, the acid generated through the pattern exposure using the first energy beam is neutralized with the base generated through the entire surface exposure using the second energy beam. On the other hand, the unexposed area of the first energy beam on the resist film attains a basic property through the entire surface exposure using the second energy beam. Contrarily, when the pattern exposure of the resist film using the second energy beam is effected and then the entire surface exposure using the first energy beam is effected, in the exposed area of the second energy beam on the resist film, the base generated through the pattern exposure using the second energy beam is neutralized with the acid generated through the entire surface exposure using the first energy beam. On the other hand, the unexposed area of the second energy beam on the resist film attains an acidic property through the entire surface exposure using the first energy beam. Accordingly, the positive type surface imaging process can be realized.
Furthermore, since the third pattern forming material comprises the copolymer including the first group for generating the acid through the irradiation with the first energy beam and the second group for generating the base through the irradiation with the second energy beam, the acid or the base cannot be generated until the irradiation with the energy beam, namely, the resist film remains to be neutral until the irradiation with the energy beam. Accordingly, the pattern forming material can be prevented from being changed in its property by an acid or a base during pre-baking, resulting in forming a stable resist film.
The first group in the third pattern forming material is preferably a group for generating sulfonic acid. In this case, when the pattern exposure is effected by using the first energy beam, owing to the strong acidic property of sulfonic acid, the exposed area of the first energy beam on the resist film can be completely neutralized, while the unexposed area of the first energy beam on the resist film retains the basic property. Accordingly, merely the unexposed area of the first energy beam on the resist film can selectively retain the basic property. Contrarily, when the pattern exposure is effected by using the second energy beam, the unexposed area of the second energy beam on the resist film can exhibit a strong catalytic function in the formation of the oxide film. Accordingly, merely the unexposed area of the second energy beam on the resist film can selectively retain the strong acidic property.
The copolymer in the third pattern forming material is preferably a binary copolymer represented by the following general formula or a ternary or higher copolymer obtained by further polymerizing the binary copolymer with another group: 
wherein R9 indicates a hydrogen atom or an alkyl group; R10 and R11 independently indicate a hydrogen atom, an alkyl group, a phenyl group or an alkenyl group, or together indicate a cyclic alkyl group, a cyclic alkenyl group, a cyclic alkyl group having a phenyl group or a cyclic alkenyl group having a phenyl group; R12 indicates a hydrogen atom or an alkyl group; R13 and R14 independently indicate a hydrogen atom, an alkyl group, a phenyl group or an alkenyl group, or together indicate a cyclic alkyl group, a cyclic alkenyl group, a cyclic alkyl group having a phenyl group or a cyclic alkenyl group having a phenyl group; x satisfies a relationship of 0 less than x less than 1; and y satisfies a relationship of 0 less than y less than 1.
In this case, sulfonic acid having a strong acidic property is generated through the irradiation of the resist film with the first energy beam, and amine having a strong basic property is generated through the irradiation with the second energy beam. Therefore, when the pattern exposure is effected by using the first energy beam, the unexposed area of the first energy beam on the resist film retains the strong basic property, while the exposed area of the first energy beam on the resist film can be completely neutralized. Contrarily, when the pattern exposure is effected by using the second energy beam, the unexposed area of the second energy beam on the resist film retains the strong acidic property, while the exposed area of the second energy beam on the resist film can be completely neutralized.
The first pattern forming method of this invention comprises a first step of forming a resist film by coating a semiconductor substrate with a pattern forming material including a copolymer having a first group for generating a base through irradiation with an energy beam and a second group having an acidic property; a second step of selectively irradiating the resist film with the energy beam by using a mask having a desired pattern, generating the base in an exposed area on the resist film and neutralizing the generated base with the second group; a third step of supplying metal alkoxide onto the resist film and forming a metal oxide film on a surface of an unexposed area on the resist film; and a fourth step of forming a resist pattern by dry-etching the resist film by using the metal oxide film as a mask.
According to the first pattern forming method, through the irradiation of the resist film with the energy beam, the generated base is neutralized with the second group having the acidic property in the exposed area on the resist film, while the unexposed area on the resist film remains to be acidic. When the metal alkoxide is supplied to the resist film, the metal oxide film cannot be formed in the exposed area because the exposed area on the resist film has been neutralized, but the metal oxide film is selectively formed in the unexposed area on the resist film. Accordingly, through the dry etching of the resist film using the metal oxide film as a mask, it is possible to form a fine-line positive type resist pattern having a satisfactory shape.
Furthermore, according to the first pattern forming method, the acid works as the catalyst in the formation of the metal oxide film in the unexposed area on the resist film, and hence, the resultant metal oxide film can attain a high density and sufficient strength.
In the first pattern forming method, the third step preferably includes a step of allowing the unexposed area on the resist film to adsorb water. In this case, since water can be diffused into a deep portion from the surface of the unexposed area on the resist film, the metal oxide film formed on the surface of the unexposed area on the resist film can attain a large thickness.
In the first pattern forming method, the second group is preferably a group including a sulfonic acid group. In this case, owing to the strong acidic property of sulfonic acid, it is possible to form the metal oxide film having a sufficient density in the unexposed area on the resist film by using the strong catalytic function of sulfonic acid. As a result, the selectivity in the dry etching can be improved. Thus, it is possible to form a more fine-line positive type resist pattern having a satisfactory shape.
The copolymer used in the first pattern forming method is preferably a binary copolymer represented by the following general formula or a ternary or higher copolymer obtained by further polymerizing the binary copolymer with another group: 
wherein R1 indicates a hydrogen atom or an alkyl group; R2 and R3 independently indicate a hydrogen atom, an alkyl group, a phenyl group or an alkenyl group, or together indicate a cyclic alkyl group, a cyclic alkenyl group, a cyclic alkyl group having a phenyl group or a cyclic alkenyl group having a phenyl group; R4 indicates a hydrogen atom or an alkyl group; x satisfies a relationship of 0 less than x less than 1; and y satisfies a relationship of 0 less than y less than 1.
In this case, since sulfonic acid can exhibit its strong catalytic function in the formation of the metal oxide film in the unexposed area on the resist film, the unexposed area on the resist film can selectively retain the strong acidic property. Therefore, the metal oxide film having a sufficient density can be formed by supplying the metal alkoxide. Furthermore, in the exposed area on the resist film, since amine having a strong basic property is generated, sulfonic acid having a strong acidic property can be completely neutralized. Therefore, the metal oxide film cannot be formed in the exposed area. In this manner, the selectivity in the dry etching is high, and hence, it is possible to form a more fine-line positive type resist pattern having a satisfactory shape.
The second pattern forming method of this invention comprises a first step of forming a resist film by coating a semiconductor substrate with a pattern forming material including a copolymer having a first group for generating an acid through irradiation with an energy beam and a second group having a basic property; a second step of selectively irradiating the resist film with the energy beam by using a mask having a desired pattern, generating the acid in an exposed area on the resist film and neutralizing the generated acid with the second group; a third step of supplying metal alkoxide onto the resist film and forming a metal oxide film on a surface of an unexposed area on the resist film; and a fourth step of forming a resist pattern by dry-etching the resist film by using the metal oxide film as a mask.
According to the second pattern forming method, through the irradiation of the resist film with the energy beam, the generated acid is neutralized with the second group having the basic property in the exposed area on the resist film, while the unexposed area on the resist film remains to be basic. When the metal alkoxide is supplied to the resist film, the metal oxide film cannot be formed in the exposed area because the exposed area on the resist film has been neutralized, but the metal oxide film is selectively formed in the unexposed area on the resist film. Accordingly, through the dry etching of the resist film using the metal oxide film as a mask, it is possible to form a fine-line positive type resist pattern having a satisfactory shape.
Furthermore, according to the second pattern forming method, the base works as a catalyst in the formation of the metal oxide film in the unexposed area on the resist film. Therefore, the speed for forming the metal oxide film can be improved, resulting in improving throughput.
In the second pattern forming method, the third step preferably includes a step of allowing the unexposed area on the resist film to adsorb water. In this case, since water is diffused into a deep portion from the surface of the unexposed area on the resist film, the metal oxide film formed in the unexposed area on the resist film can attain a large thickness.
In the second pattern forming method, the first group is preferably a group for generating sulfonic acid. In this case, owing to the strong acidic property of sulfonic acid, the exposed area on the resist film can be completely neutralized, while the unexposed area on the resist film retains the basic property. Therefore, the metal oxide film can be formed merely in the unexposed area on the resist film with high selectivity. Accordingly, it is possible to form a more fine-line positive resist pattern having a satisfactory shape.
The copolymer used in the second pattern forming method is preferably a binary copolymer represented by the following general formula or a ternary or higher copolymer obtained by further polymerizing the binary copolymer with another group: 
wherein R5 indicates a hydrogen atom or an alkyl group; R6 and R7 independently indicate a hydrogen atom, an alkyl group, a phenyl group or an alkenyl group, or together indicate a cyclic alkyl group, a cyclic alkenyl group, a cyclic alkyl group having a phenyl group or a cyclic alkenyl group having a phenyl group; R8 indicates a hydrogen atom or an alkyl group; x satisfies a relationship of 0 less than x less than 1; and y satisfies a relationship of 0 less than y less than 1.
In this case, in the unexposed area on the resist film, amine exhibits its strong catalytic function, and hence, the metal oxide film with a sufficient density can be formed. On the other hand, in the exposed area on the resist film, since sulfonic acid having a strong acidic property is generated, amine having a strong basic property can be completely neutralized. As a result, the selectivity in the dry etching is very high, and it is possible to form a more fine-line positive resist pattern having a satisfactory shape.
The third pattern forming method of this invention comprises a first step of forming a resist film by coating a semiconductor substrate with a pattern forming material including a copolymer having a first group for generating an acid through irradiation with a first energy beam having a first energy band and a second group for generating a base through irradiation with a second energy beam having a second energy band different from the first energy band; a second step of selectively irradiating the resist film with the first energy beam by using a mask having a desired pattern, and generating the acid in an exposed area of the first energy beam on the resist film; a third step of irradiating an entire surface of the resist film with the second energy beam, generating the base on the entire surface of the resist film, and neutralizing the generated base with the acid generated in the exposed area of the first energy beam on the resist film; a fourth step of supplying metal alkoxide onto the resist film and forming a metal oxide film on a surface of an unexposed area of the first energy beam on the resist film; and a fifth step of forming a resist pattern by dry-etching the resist film by using the metal oxide film as a mask.
According to the third pattern forming method, in the exposed area of the first energy beam on the resist film, since the acid generated through the pattern exposure using the first energy beam is neutralized with the base generated through the entire surface exposure using the second energy beam, the metal oxide film cannot be formed in the exposed area. On the other hand, in the unexposed area of the first energy beam on the resist film, since the base is generated through the entire surface exposure using the second energy beam, the metal oxide film can be formed owing to the catalytic function of the base by supplying the metal alkoxide to the resist film. Accordingly, through the dry etching of the resist film using the metal oxide film as a mask, a positive type resist pattern can be formed.
Furthermore, according to the third pattern forming method, since the base works as the catalyst in the formation of the metal oxide film in the unexposed area of the first energy beam on the resist film, the speed for forming the metal oxide film can be improved, resulting in improving the throughput.
In the third pattern forming method, the first group is preferably a group for generating sulfonic acid. In this case, owing to the strong acidic property of sulfonic acid, the exposed area of the first energy beam on the resist film can be completely neutralized, while the unexposed area of the first energy beam on the resist film retains the basic property. Accordingly, the metal oxide film can be formed merely in the unexposed area of the first energy beam on the resist film with very high selectivity. As a result, it is possible to form a more fine-line positive type resist pattern having a satisfactory shape.
The fourth pattern forming method of this invention comprises a first step of forming a resist film by coating a semiconductor substrate with a pattern forming material including a copolymer having a first group for generating a base through irradiation with a first energy beam having a first energy band and a second group for generating an acid through irradiation with a second energy beam having a second energy band different from the first energy band; a second step of selectively irradiating the resist film with the first energy beam by using a mask having a desired pattern, and generating the base in an exposed area of the first energy beam on the resist film; a third step of irradiating an entire surface of the resist film with the second energy beam, generating the acid on the entire surface of the resist film, and neutralizing the generated acid with the base generated in the exposed area of the first energy beam on the resist film; a fourth step of supplying metal alkoxide onto the resist film and forming a metal oxide film on a surface of an unexposed area of the first energy beam on the resist film; and a fifth step of forming a resist pattern by dry-etching the resist film by using the metal oxide film as a mask.
According to the fourth pattern forming method, in the exposed area of the first energy beam on the resist film, since the base generated through the pattern exposure using the first energy beam is neutralized with the acid generated through the entire surface exposure using the second energy beam, the metal oxide film cannot be formed in the exposed area. On the other hand, in the unexposed area of the first energy beam on the resist film, since the acid is generated through the entire surface exposure using the second energy beam, the metal oxide film can be formed owing to the catalytic function of the acid by supplying the metal alkoxide. Accordingly, through the dry etching of the resist film using the metal oxide film as a mask, a positive type resist pattern can be formed.
Furthermore, according to the fourth pattern forming method, since the metal oxide film can be formed owing to the catalytic function of the acid in the unexposed area of the first energy beam on the resist film, the resultant metal oxide film can attain a high density and sufficient strength.
In the fourth pattern forming method, the second group is preferably a group for generating sulfonic acid. In this case, since sulfonic acid is a strong acid, it is possible to form a metal oxide film having a sufficient density in the unexposed area of the first energy beam on the resist film owing to the strong catalytic function of sulfonic acid. As a result, the selectivity in the dry etching is high, and it is possible to form a more fine-line positive type resist pattern having a satisfactory shape.
In the third or fourth pattern forming method, the fourth step preferably includes a step of allowing the unexposed area on the resist film to adsorb water. In this case, since water is diffused into a deep portion from the surface of the unexposed area of the first energy beam on the resist film, the metal oxide film formed in the unexposed area can attain a large thickness.
The copolymer used in the third or fourth pattern forming method is preferably a binary copolymer represented by the following general formula or a ternary or higher copolymer obtained by further polymerizing the binary copolymer with another group: 
wherein R9 indicates a hydrogen atom or an alkyl group; R10 and R11 independently indicate a hydrogen atom, an alkyl group, a phenyl group or an alkenyl group, or together indicate a cyclic alkyl group, a cyclic alkenyl group, a cyclic alkyl group having a phenyl group or a cyclic alkenyl group having a phenyl group; R12 indicates a hydrogen atom or an alkyl group; R13 and R14 independently indicate a hydrogen atom, an alkyl group, a phenyl group or an alkenyl group, or together indicate a cyclic alkyl group, a cyclic alkenyl group, a cyclic alkyl group having a phenyl group or a cyclic alkenyl group having a phenyl group; x satisfies a relationship of 0 less than x less than 1; and y satisfies a relationship of 0 less than y less than 1.
When the copolymer represented by Chemical Formula 6 is used in the third pattern forming method, since sulfonic acid generated through the pattern exposure using the first energy beam is neutralized with amine generated through the entire surface exposure using the second energy beam, the metal oxide film cannot be formed in the exposed area of the first energy beam on the resist film. On the other hand, in the unexposed area of the first energy beam on the resist film, since amine having a strong basic property is generated through the entire surface exposure using the second energy beam, the metal oxide film with a sufficient density can be formed by supplying the metal alkoxide to the resist film. Accordingly, the selectivity in the dry etching is very high, and it is possible to form a more fine-line positive resist pattern having a satisfactory shape.
When the copolymer represented by Chemical Formula 6 is used in the fourth pattern forming method, since amine generated through the pattern exposure using the first energy beam is neutralized with sulfonic acid generated through the entire surface exposure using the second energy beam, the metal oxide film cannot be formed in the exposed area of the first energy beam on the resist film. On the other hand, in the unexposed area of the first energy beam on the resist film, since sulfonic acid having a strong acidic property is generated through the entire surface exposure using the second energy beam, the metal oxide film with a sufficient density can be formed by supplying the metal alkoxide. Accordingly, the selectivity in the dry etching is very high, and it is possible to form a more fine-line positive type resist pattern having a satisfactory shape.